The present invention relates generally to internal combustion engines and, more particularly, to an automobile engine misfire detection system and method based on mathematical models for spark-ignited engines and misfire prediction.
Engine misfire can occur for several reasons such as the absence of spark in the cylinder, poor fuel metering, inadequate compression, or other similar conditions. As a result of engine misfires, an increased amount of unburned combustion byproducts are passed through the catalytic converter. Over time, engine misfiring can cause damage to the catalyst in the catalytic converter and, consequently, increase the amount of combustion byproducts emitted into the atmosphere.
Because engine misfire can effect engine emissions, government regulatory agencies require that the vehicle fuel control system detect and indicate emission malfunctions such as misfiring. This engine misfiring information is typically collected and stored in computer memory associated with the vehicle engine for later downloading and analysis at a service center.
A variety of schemes have been developed for misfire detection including: (1) ionization current monitoring, (2) combustion pressure detection--which requires a pressure transducer in every engine cylinder, (3) cylinder pressure reconstruction using crankshaft speed variation, and (4) measurement of crankshaft angular velocity as well as other techniques based on crankshaft angular velocity and/or acceleration. There are several drawbacks to these present misfire detection methods. The first two methods require additional sensors or hardware which increase the system cost and complexity. In addition, the misfire detection methods based on crankshaft velocity or acceleration are prone to detection errors because they are based on four major assumptions: (1) a constant co-efficient driveline model, (2) a constant load torque, (3) a torsionally rigid crankshaft, and (4) non-overlapping firing pulses. These assumptions can result in a normal combustion cycle being counted as a misfire, and a misfired combustion cycle going undetected.